1. Field of the Invention
The present invention relates to a method for producing a rare earth alloy magnet powder which exhibits stable and superior magnetic properties.
2. Related Art
Heretofore, there has been well known a method for producing a rare earth alloy magnet powder comprising:
a rare earth element inclusive of yttrium (Y) (which will be hereinafter represented by "R"); PA1 iron (Fe) which may be partially substituted with cobalt (Co) (which will be hereinafter represented by "T"); and PA1 boron (B). PA1 melting and casting a R-T-B alloy ("R", "T" and "B" are as defined above) in which "R", "T" and boron (B) are included as main ingredients to form an ingot; PA1 subjecting the ingot to a homogenization treatment while the temperature of the ingot is maintained from 600.degree. C. to 1200.degree. C.; PA1 placing the homogenized ingot and a regenerative material (heat-storage material) in a heat treating furnace; PA1 occluding hydrogen into the homogenized ingot in the heat treating furnace kept under a hydrogen atmosphere by heating the furnace from room temperature to 500.degree. C., followed by maintaining the furnace at a temperature in a range between 750.degree. C. and 950.degree. C. to form a hydrogen-occluded ingot, wherein a phase transformation occurs in the ingot; PA1 subjecting the hydrogen-occluded ingot to a dehydrogenation while maintaining the furnace in a vacuum at a temperature in a range between 750.degree. C. and 950.degree. C., wherein a phase transformation occurs in the ingot; and PA1 cooling and crushing the dehydrogenated ingot to obtain a R-T-B alloy magnet powder. PA1 (a) It is difficult for the regenerative material to contact all ingots. The ingots in contact with the regenerative material can be maintained at a desired temperature, while the ingots away from the regenerative material cannot avoid reducing the temperature, leading to degraded magnetic properties of the magnet powder. PA1 (b) A large heat treating furnace with a large volume is needed in order to place the regenerative material therein. With a large volume of the heat treating furnace, in addition to the length of time required for changing the atmosphere from a hydrogen atmosphere to a vacuum, the scale of the facility for processing a given quantity of ingots becomes large, leading to poor productivity. PA1 (c) The treated ingots in the furnace need to be separated from the regenerative material before the crushing step. During the separation of the ingots from the regenerative material, a part of the regenerative material may contaminate the separated ingot, causing a degradation in magnetic properties of the final product. PA1 (a) preparing a rare earth alloy material represented by R-T-B alloy, wherein R is a rare earth element inclusive of yttrium (Y) ; T is iron (Fe) which may be partially substituted with cobalt (Co); and B is boron (B); PA1 (b) subsequently subjecting the alloy material to a homogenization treatment while maintaining the alloy at a temperature in a range between 600.degree. C. and 1200.degree. C. to form a homogenized alloy; PA1 (c) preparing a vacuum tube furnace; PA1 (d) subsequently placing the homogenized alloy in the vacuum tube furnace; PA1 (e) subsequently occluding hydrogen into the homogenized alloy in the vacuum tube furnace by heating the furnace from room temperature to 500.degree. C. followed by maintaining the furnace at a temperature in a range between 750.degree. C. and 950.degree. C. to form a hydrogen-occluded alloy; PA1 (f) subsequently subjecting the hydrogen-occluded alloy to dehydrogenation while maintaining the alloy, placed in the furnace in a vacuum, at a temperature in a range between 750.degree. C. and 950.degree. C. to form a dehydrogenated alloy, wherein the alloy maintains a temperature drop of at most 50.degree. C. due to an endothermic reaction occurring during the dehydrogenation; and PA1 (g) cooling and crushing the dehydrogenated alloy to obtain a R-T-B rare earth alloy magnet powder comprising particles, each particle having an aggregated structure of fine recrystallized grains of the ferromagnetic compound.
The conventional method as disclosed in copending U.S. Patent Application Ser. No. 560,594 and U.S. Pat. No. 4,981,532 comprises the successive steps of:
In general, the phase transformation which occurs during the dehydrogenation is an endothermic reaction, as described in copending U.S. Patent Application Ser. No. 560,594, so that the temperature of the ingot is lowered, whereby thus obtained R-T-B alloy magnet powder suffers degradation in magnetic properties. In order to avoid this disadvantage, a regenerative material is employed to compensate for the temperature drop due to the endothermic reaction in the conventional art as described above.
However, the conventional art using a regenerative material has the following drawbacks: